Fix #538: Give higher priority to out parameters when naming variables

ICSharpCode.Decompiler.Tests/TestCases/Pretty/AnonymousTypes.cs

@@ -105,11 +105,11 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 #if CS70
 		private void AnonymousTypeOutVar()
 		{
-			InlineVarDecl(out var anon, new {
+			InlineVarDecl(out var v, new {
 				X = 1,
 				Y = 2
 			});
-			Console.WriteLine(anon.X);
+			Console.WriteLine(v.X);
 		}
 #endif
 

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.cs

@@ -280,7 +280,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			item = null;
 		}
 
-		private static void Operation(ref int item)
+		private static void Operation(ref int i)
 		{
 		}
 
@@ -417,11 +417,11 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			foreach (int item in items) {
 #if ROSLYN && OPT
 				// The variable name differs based on whether roslyn optimizes out the 'item' variable
-				int current = item;
+				int i = item;
-				Operation(ref current);
+				Operation(ref i);
 #else
-				int num = item;
+				int i = item;
-				Operation(ref num);
+				Operation(ref i);
 #endif
 			}
 		}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.il

@@ -693,7 +693,7 @@
     IL_0004:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       2 (0x2)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.mcs.il

@@ -653,7 +653,7 @@
     IL_0003:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       1 (0x1)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.opt.il

@@ -603,7 +603,7 @@
     IL_0003:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       1 (0x1)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.opt.mcs.il

@@ -653,7 +653,7 @@
     IL_0003:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       1 (0x1)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.opt.roslyn.il

@@ -607,7 +607,7 @@
     IL_0003:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       1 (0x1)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Loops.roslyn.il

@@ -694,7 +694,7 @@
     IL_0004:  ret
   } // end of method Loops::TryGetItem
 
-  .method private hidebysig static void  Operation(int32& item) cil managed
+  .method private hidebysig static void  Operation(int32& i) cil managed
   {
     // Code size       2 (0x2)
     .maxstack  8

ICSharpCode.Decompiler.Tests/TestCases/Pretty/PInvoke.cs

@@ -92,8 +92,8 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		public void CallMethodWithInOutParameter()
 		{
-			int num = 0;
+			int argp = 0;
-			ioctlsocket(IntPtr.Zero, 0, ref num);
+			ioctlsocket(IntPtr.Zero, 0, ref argp);
 		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -259,6 +259,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					}
 				}
 			}
+			if (string.IsNullOrEmpty(proposedName)) {
+				var proposedNameForAddress = variable.AddressInstructions.OfType<LdLoca>()
+					.Select(arg => arg.Parent is CallInstruction c ? GetNameFromParameter(c.GetParameter(arg.ChildIndex)) : null)
+					.Where(arg => !string.IsNullOrWhiteSpace(arg))
+					.Except(currentFieldNames).ToList();
+				if (proposedNameForAddress.Count > 0) {
+					proposedName = proposedNameForAddress[0];
+				}
+			}
 			if (string.IsNullOrEmpty(proposedName)) {
 				var proposedNameForStores = variable.StoreInstructions.OfType<StLoc>()
 					.Select(expr => GetNameFromInstruction(expr.Value))
@@ -301,6 +310,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
+		static readonly FullTypeName DllImportAttributeName = new TopLevelTypeName("System.Runtime.InteropServices", "DllImportAttribute");
+
+		static string GetNameFromParameter(IParameter param)
+		{
+			if (param == null || !(param.Owner is IMethod method))
+				return string.Empty;
+			string name = param.Name;
+			// Special case for DllImports:
+			if (name.Length > 1 && name.StartsWith("p", StringComparison.Ordinal) && method.GetAttribute(DllImportAttributeName) != null) {
+				return name.Substring(1);
+			}
+			return name;
+		}
+
 		static string GetNameFromInstruction(ILInstruction inst)
 		{
 			switch (inst) {